Does your app solve a problem you had, or was the problem faced by others and it was popular?

I have seen people advicing each other to build a saas around your own problems. But, the question is, anyone who is starting out or hasn't got a problem yet, what are they gonna build?

Apart from this, there are many people who build passion projects and many others just build what is trending.

In my case, the first saas I build was more of a project which excited me and it does not have a market. And the second saas I built was a problem, but it has way more solutions than people asked.

The second saas was around LinkedIn and it has various competitors, that the market seem impossible to enter for someone not good in marketing and was a newbie.

Now, I research for what people complain and would build something around it as I know there is a potential demand. What have you done, solving your own problem and then commercializing it or picking a popular problem and working on it?